The present invention relates to an apparatus for measuring a load at a shaft member having opposite ends on which the weight of a vehicle such as a truck is dispersively imposed.
The measurement of a load of a vehicle is performed mainly for a large-sized vehicle such as a truck, for example, for the purpose of preventing traffic accidents such as rolling accidents caused by overload, etc., and preventing acceleration of deterioration of the vehicle and a road surface. Conventionally, there is used a method in which the measurement of a load of a vehicle is performed in the condition that the vehicle, which is a subject of the measurement, is placed on a platform weighing machine commonly called "Kankan". Recently, the conventional method is shifted to a method in which the measurement of a load of a vehicle is performed by a load measuring apparatus which is mounted on the vehicle per se without necessity of such an equipment and installation space.
As the aforementioned on-vehicle type load measuring apparatuses, the present applicant has already proposed some load measuring apparatuses using load measurement sensing devices such as strain gauge sensors attached to circular-arc-like leaf springs interposed between carrier frames and axles.
As one of them, a structure for attaching vehicle load measurement sensing devices has been proposed in Japanese Patent Unexamined Publication No. Hei. 8-313332 with respect to the arrangement of the sensing devices.
As shown in FIG. 6 which is an explanatory view, in this attachment structure, a shackle pin 5 is passed through not only insertion holes 33b of opposite sides 33a of a bracket 33 connected to a carrier frame (not shown) of a vehicle but also an insertion hole 34a of a shackle 34 connected to an end portion of a leaf spring (not shown) and inserted between the opposite sides 33a of the bracket 33. Accordingly, the bracket 33 and the shackle 34 are connected to each other by the shackle pin 5 so as to be rockable.
A sensing device 7 is disposed so as to be received in one end portion of the shackle pin 5 and so as to be laid between one side 33a of the bracket 33 and the bracket 33. Another sensing device 7 is disposed so as to be received in the other end portion of the shackle pin 5 and so as to be laid between the other side 33a of the bracket 33 and the bracket 33. The load of the vehicle imposed on the shackle 34 from the opposite sides 33a of the bracket 33 is measured on the basis of the sum of outputs of the two sensing devices 7, 7.
Not only in the case where a load of a vehicle is imposed on the shackle pin 5 while the load is allocated to the opposite sides 33a of the bracket 33 so as to be equally divided into halves as shown in FIG. 6, but also in the case where a load of a vehicle is imposed on the shackle pin 5 while the load is allocated to the opposite sides 33a of the bracket 33 so as to be biased to one side, for example, in the condition in which three-fourths of the load of the vehicle is applied to one side 33a of the bracket 33 and one-fourth as the residual part is applied to the other side 33a of the bracket 33 as shown in FIG. 7 which is an explanatory view, the aforementioned structure of attachment of vehicle load measurement sensing devices according to Japanese Patent Unexamined Publication Hei. 8-313332 is excellent in that the load can be measured substantially exactly compared with the case where only one sensing device is received in a shackle pin to measure a load.
However, if there is a difference in characteristic between the two sensing devices 7, 7 received in the shackle pin 5, and if there is a difference between the output signals of the sensing devices 7, 7 even in the case where the same load is imposed, the sum of outputs of the two sensing devices 7, 7 varies correspondingly to the imbalance between split loads imposed on the opposite sides 33a of the bracket 33 in spite of the constant load when the load of the vehicle is unequally allocated to the sides 33a of the bracket 33. Accordingly, the load cannot be measured exactly.